The field of art to which this invention pertains is polyacetals and a process for improving the adhesion to polyacetal articles.
Polyacetal resins have excellent thermal, mechanical and chemical properties, such as very high strength and toughness per unit weight and good solvent resistance. Due to such properties, polyacetals (polyoxymethylenes) can be used in a wide variety of applications, such as serving as a substitute for metals in certain automobile parts. However, conventional top-coating compositions and primers do not readily adhere to polyoxymethylenes. Generally, polyacetal plastics have low surface energies thereby making it difficult for water or adhesives to wet the surface to form strong bonds. As a result, it is necessary to improve the adhesion to polyacetal structures so that adhesives and coatings can be more readily applied to polyacetal articles. To improve the adhesion, it is necessary to treat polyacetal articles so that plating or coating is more readily achieved. In the prior art, different approaches have been taken in order to improve the adhesion to articles prepared from polyoxymethylenes.
For example, in Canadian Patent No. 744,024, a primer coating composition for acetal plastic surfaces is disclosed. The composition is comprised of a film forming polymer, a phosphoric acid ester, and a boron trifluoride catalyst. The composition is applied to an acetal article and then baked to form a primer coating to which decorative coatings can be applied.
U.S. Pat. No. 3,141,789 discloses a coating composition for coating polyoxymethylene. The composition is comprised of a nitrocellulose, a sulfonamide, a formaldehyde resin former and a non-volatile acid. After the composition is applied to a polyoxymethylene substrate, it is baked to form a coating to which a variety of top coats can be applied.
U.S. Pat. No. 3,595,718 discloses a process for etching plastic surfaces, such as acetal surfaces. A high surface carrier, such as diatomaceous earth, that has been impregnated with an etching agent, such as an organic or inorganic acid, is used to treat a plastic article. The article can be buried in a bed of the impregnated carrier. After treatment, the article is more receptive to coatings.
In U.S. Pat. No. 4,418,162, a method for treating the surface of polyacetal resin articles is disclosed. The article is treated with an acidic solution containing hydrochloric and sulfuric acid. After such treatment, the article can be non-electrically plated with a nickel plating solution. The patent also discloses that the polyacetal resin preferably contains calcium carbonate.
However, none of the patents discloses that a glass containing can be treated with organosilanes and titanates to improve adhesion to the article.
It is an object of this invention to improve adhesion to glass containing polyacetal articles.
It is another object of this invention to facilitate the application of coatings on glass containing polyacetal articles.
It is a further object of this invention to provide a means for uniformly coating glass containing polyacetal articles with adhesives and traditional coatings.
These objects are obtained by the process of this invention.